During the middle Holocene (between 6000 and 9000 years ago), a general warm period followed the disappearance of glacial ice with temperatures peaking. Macrofossil analysis and radiocarbon dating of peat cores have been used to reconstruct the permafrost distribution in western Canada 6000 years ago. The results of this analysis suggest that mean annual temperatures were about 5°C warmer than present and the southern limit of permafrost was 300 to 500 km northward of its current position. Much of the present discontinuous permafrost zone may have been free of permafrost. Where permafrost did exist during this time, active layer thickness was probably greater than at present. Many thermokarst lakes also developed in the Mackenzie Delta during this time. Cooler conditions followed the mid-Holocene warm period and permafrost became more extensive. Permafrost was probably established in northwestern Alberta by 3700 years ago and the climate at this time probably resembled the present climate regime. In the Mackenzie Delta region, permafrost aggradation (growth) and pingo development occurred in response to the deterioration in climate that began about 5000 BP (Smith, Burgess & Heginbottom, 2001).
The exact initiation and termination of the Holocene Warm Period (with subsequent permafrost growth) varies geographically across the Canadian Arctic (Figure 1). It is estimated that the warm period began first in Greenland, Alaska and western Canada followed by northeastern Canadian regions. The termination followed a similar pattern (Kaufman et al., 2004).
Material for this section was provided by Sharon Smith and Margo Burgess of the Geological Survey of Canada and Maren Pauly (Department of Geography, University of Waterloo)